A planar terahertz (THz) narrow bandpass filter for the sensing of small amounts of overlaid dielectrics is presented. A two-dimensional (2D) periodic array of four sub-wavelength rectangular split-ring resonators (SRRs) is developed on a benzocyclobutene (BCB) substrate to realize the novel compact, low insertion-loss, and narrow bandpass microstrip filter with the center frequency of 1 THz and 3-dB bandwidth of 6.2 GHz. Due to center frequency shifts occurs with the change of equivalent permittivities at the surface of the filter when it covered by dielectrics of different permittivity and thickness, this narrow bandpass filter is especially suitable for detecting the properties of overlaid dielectrics.
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